Assembly for grinding electrodes and grinding wheel

ABSTRACT

A device for processing welding electrodes with a grinding wheel having a selected grain size driven by a driving motor with a shaft, which runs in a housing, wherein at least one opening is provided in the housing for guiding a welding electrode for processing in a defined position relative to the grinding wheel is characterized in that a recess adapted to the grain size of the grinding material is provided in the range provided for grinding on the surface of the grinding wheel which is coated with grinding material.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is filed herewith for the U.S. National Stageunder 35 U.S.C. §371 and claims priority to PCT applicationPCT/EP2010/065341, with an international filing date of 13 Oct. 2010 anda Convention priority date of 10 Dec. 2009. The contents of thisapplication are incorporated in their entirety herein. This applicationis also related to U.S. non-provisional patent application titledAssembly Kit For Upgrading An Electrode Grinding Device And ElectrodeGrinding Device, filed concurrently herewith.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD

The invention relates to a device for processing welding electrodes witha grinding wheel having a selected grain size driven by a driving motorwith a shaft, which runs in a housing, wherein at least one opening isprovided in the housing for guiding a welding electrode for processingin a defined position relative to the grinding wheel.

Welding electrodes consist of very hard and high-temperature resistantmaterial, such as tungsten. There are welding electrodes with differentcross sections. The welding electrodes have a tip or edge at one end.This shape of the welding electrode depends on the respectiveapplication. The tips of the welding electrodes wear out duringoperation.

Welding electrodes can be bought without shaping or with a ready-madetip. After use the tip or the shape is worn out. The welding electrodesare then reshaped or disposed of. Due to the precious material this isexpensive.

BACKGROUND OF THE INVENTION

It is known to grind electrodes. This is commonly effected manually withopen grinding- or separating wheels. Such methods are imprecise anddangerous. Furthermore, there are devices with open grinding wheelsknown where the welding electrodes are guided through a guiding sleevewith a certain angle relative to the grinding wheel. Such devices arealso expensive. In particular, it is expensive to adapt such a device tovarious types of welding electrodes or for different tips or cuttingshapes. In particular, this requires the exchange of the guidingsleeves.

A device where electrodes can be produced with a plurality (for example6) of different electrode diameters with a plurality of different tipangles (for example 4) with many lengths is a valuable, cost-saving aid.

DE 100 10 520 A1 discloses a device for processing welding electrodeswith a grinding wheel. The grinding wheel rotates in a grinding wheelhousing. The device furthermore is provided with an additional housingportion which is adapted to be fixed to the grinding wheel housing andwhich is provided with at least one opening for guiding a weldingelectrode for processing in a defined position relative to the grindingwheel. The plane of the grinding wheel is essentially the separatingplane between the grinding wheel housing and the additional housingportion. The additional housing portion can be provided with a pluralityof adjacent, different openings for receiving different kinds of weldingelectrodes. The additional housing portion can, however, also beprovided with a plurality of adjacent openings having an axis cuttingthe plane of the grinding wheel under different angles. A radial slitcan be formed in the grinding wheel housing extending along the frontend of the housing, which is used to receive a welding electrode forcutting at the outer perimeter of the grinding wheel. The grinding wheelof the disclosed device is fixed to a grinding wheel reception which inturn is connected to a driving shaft of a driving motor. The entiredevice forms a portable unit.

US 2004/0127149 A1 discloses an assembly where two parallel grindingwheels with different grain size are used. A first grinding wheelrotates in a space between the motor unit and a first housing portion.The second grinding wheel rotates in a second space between the firsthousing portion and the second housing portion. The housing portions areprovided with openings for guiding the welding electrodes. The knownassembly enables the use of different grinding wheels without the needof exchange.

Further to a motor in a motor unit the assembly makes use of furtherhousing portions: a motor flange directly screwed to the motor unit andat least one housing portion provided with openings for guiding theelectrodes. The openings extend from the side of the housing portionopposite to the motor in the direction of the grinding wheel rotatingbetween the motor flange and the housing portion. Depending on theamount of grinding wheels further housing portions are added. Here alsothe openings extend from the side opposite the motor. In other words,the electrodes are always inserted into the openings in a directiontowards the motor. Depending on the amount of housing portions theassembly is relatively long and requires a long driving shaft. Severalfixing elements, such as screws, nuts, pins etc. are required for fixingthe housing portions.

US 2008/0108284 A1 discloses an assembly where two grinding wheelshaving a different grain size rotate in practically one plane in acommon space. The grinding surfaces of the known assembly are facingopposite directions. A third wheel with a larger diameter is arrangedbetween such grinding wheels. Such wheel is used for cutting electrodes.

The bore holes or openings for guiding electrodes are produced with highprecision regarding the angle. It is understood that the correspondinggrinding wheel rotates in a defined position relative to the housing.With different thicknesses or with the use of several grinding wheelsthis is not ensured anymore. In such a case the grinding angle is notthe target value.

During the production of grinding wheels the unprocessed raw disc isdipped into a bath for application of the grinding means. Accordingly,it is difficult with such a method to produce grinding wheels with adifferent grain size on the top side and bottom side. The green body isa plane disc. Depending on the grain size the finished wheel is thickerwith a rough grain size than with a small grain size. This causesdifferent overall thicknesses. The grinding plane will then not be inthe separating plane between the two housing portions for each grainsize. Due to pressure of the screw upon tightening the grinding wheelthere is a risk of bending the grinding wheel. This is not wanted.

With such known grinding wheels the best grinding results are obtainedin the outer range having the highest velocity of the grinding wheel.The grinding wheel may, however, not be any size because lateral forcesand undesired oscillations can occur at high angular rates. Furthermore,large grinding wheels require a large housing thereby rendering theassembly difficult to handle.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide an easy-to-handle grindingassembly of the above mentioned kind which is suitable for all grainsizes in the same way and which may be manufactured with smallerproduction tolerances. Furthermore, it is an object of the invention toimprove the grinding results.

According to the present invention this object is achieved in that arecess adapted to the grain size of the grinding material is provided inthe range provided for grinding on the surface of the grinding wheelwhich is coated with grinding material. The recess can be taken intoaccount already during the production of the green body. A deeper recessis required for rough grain size than with a fine grain size.

Preferably, the diameter of the green body is also adapted to the grainsize of the grinding material. Thereby, the same outer diameters areachieved for all grinding wheels. The manufacturing tolerances may thenbe smaller. The housing diameters are minimized.

Preferably, the recess extends from an uncoated center range to the edgeof the grinding wheel. The center range, which is not provided forgrinding has the same thickness in all cases. In such a way a grindingwheel is produced which has the same thickness independent of the grainsize. Thereby, the forces effective on the wheel are minimized. Thewheel always rotates in the separating plane between the two housingportions independent of the grain size. Thereby the grinding angle isobtained with high precision. The velocity of the grinding wheel is thelargest in the outer range. There, the best grinding results areobtained.

In a preferred modification of the invention it is provided that:

-   -   (a) the grinding wheel is provided with a thinner cutting edge,    -   (b) a slit is provided in the housing extending perpendicular to        the grinding wheel for cutting a welding electrode with the        cutting edge, and    -   (c) the cutting edge forms a plane laying in the plane of the        remaining portion of the grinding wheel in such a way that the        grinding wheel forms the cutting edge in the range of the        circumference without a step.

The thinner cutting edge serves to cut the electrode. A larger range isprovided for grinding by forming the cutting edge in the range of thecircumference without a step. A separate wheel having a larger diameteris not necessary. Thereby, the assembly is simplified. All wheels havethe same diameter.

In a particularly preferred embodiment of the invention two grindingwheels are provided laying on top of each other and having a differentgrain size. Thereby, fine grinding and rough grinding can be achievedwith the same device without having to exchange components of theassembly. By using grinding wheels having the same thickness it does notmatter which grain size is chosen for the grinding wheels.

Preferably, the cutting edge is provided on the side opposite to theother grinding wheel. Thereby, the larger grinding range having a largerdiameter is provided.

Further modifications of the invention are subject matter of thesubclaims. An embodiment is described below in greater detail withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exploded view of a device for grinding electrodes with twogrinding wheels;

FIG. 2 is a cross sectional view of a device for grinding electrodeswith a grinding wheel;

FIG. 3 shows the head of the assembled device with one grinding wheel ingreater detail;

FIGS. 4( a)-4(e) show cross section, side views and a perspective viewof a grinding wheel in greater detail;

FIG. 5 is a cross section of a device for grinding electrodes with twogrinding wheels; and

FIG. 6 is a detailed exploded view of the assembly with two grindingwheels as shown in FIG. 1 and FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Numeral 10 in the figures generally denotes a device for grindingwelding electrodes made of tungsten. The device 10 comprises a motorwith a motor housing 12, a motor flange 14 screwed to the motor housing12 and a cylindrical housing portion 16 mounted on the motor flange 14.The housing portion 16 is connected to the motor and the motor flange ina way which is described below in greater detail. A grinding wheelassembly 18 with grinding wheels 20 and 22 having different grain sizerotates in the range between the motor flange 14 and the housing portion16.

The flange is provided with bore holes. The motor flange 14 is screwedto the motor housing 12 with screws extending through such bore holes asshown in FIG. 1. The housing portion 16 is tightly connected to themotor flange 14 with a screw 13 and a nut 15. For this purpose thehousing portion 16 has a bore hole and the motor flange a receptacle forthe nut 15.

A disc-shaped recess is provided in the end 26 of the motor flange 14opposite the motor end. This recess serves to receive the grinding wheel22. The shaft 30 screwing the grinding wheel assembly 18 to the motor,simultaneously serves as motor shaft.

The shaft 30 has an upper portion 28. Furthermore, the shaft 30 has abore hole 32 with an inner thread in the upper portion 28. In addition,an extra-centric pin 34 is fixed to the upper portion 28. The grindingwheels 20 and 22 of the grinding wheel assembly 18 are provided with acentral bore hole 38 and an extra-centric bore hole 40 connectedthereto. They can be seen well in FIG. 4 a and FIG. 4 b. The grindingwheels 20 and 22—or in case of only one grinding wheel as shown in FIG.3, the grinding wheel 20—are mounted on the shaft 30 and screwedtogether with a screw 36 in such a way that the central bore hole 38 isaligned with the axial bore hole 32 in the shaft 30 and that the pin 34extends through the extra-centric bore hole 40 in the grinding wheel 22on the side of the motor. The grinding wheels rotate about the axis ofthe bore holes 32 and 38 while the pin 34 engages with the bore hole 40and transfers the driving power on the grinding wheel assembly 18. Acentering sleeve 37 is inserted from above through the center bore holes38 of the two grinding wheels 20 and 22. The upper end of the centeringsleeve 37 opposite to the motor end is provided with a receptacle 39 forthe screw head of the screw 36. The centering sleeve 37 ensures thatboth grinding wheels 20 and 22 rotate about the same axis. The centeringsleeve 37 is provided with a projecting nose 41. The nose engages in theextra-centric bore holes 40 of the grinding wheels 20 and 22. In such away the driving power of the motor is transferred from the first,motor-side grinding wheel 22 through the centering sleeve 37 to thesecond, upper grinding wheel 20. The centering sleeve 37 is screwed tothe shaft together with the grinding wheels 20 and 22 with the screw 36.This can be particularly well seen in FIG. 3.

In the embodiment shown in FIGS. 1, 5 and 6 with two grinding wheels 20and 22 the grinding wheel assembly 18 comprises a grinding wheel 20 withrough grains and a grinding wheel 22 with fine grains which is otherwisethe same. The grinding wheels 20 have a particularly sharp edge 42. Thisedge 42 serves to cut electrodes with improved cutting behavior. Theedge is integrated in grinding wheel 20 in such a way that one of itssides lies in the grinding plane. This can be well seen in FIG. 4 c andFIG. 4 d. In such a way one of the grinding surfaces, i.e. grindingsurface 44, is larger on the side of the edge 42, than the oppositegrinding surface 46. It is understood, that with the use of two grindingwheels, as it is the case in the embodiment shown in FIGS. 1, 5 and 6,the grinding wheels are arranged in such a way that the larger grindingsurfaces are on the outside. Thereby, a larger grinding range isprovided. The outer range has a higher local velocity and a largergrinding range. Accordingly, a better grinding result can be obtained.

The grinding wheels 20 and 22 are made of a green body 48. The greenbody 48 is dipped into a bath with grinding material. The grindingmaterial, for example diamond grains of a selected grain size, sticks tothe green body. Depending on the grain size different green bodies areused. Each green body has a center range 50 which is not coated. Thebore holes 38 and 40 are provided in such uncoated center range 50. Thecenter range 50 has a standard thickness which is the same for all greenbodies independent from the grain size. Accordingly, the wheels willcompletely lay upon each other in this range if several wheels are used.Furthermore, the green bodies are provided with a wide, area-like recessextending up to the edge. The recess quasi forms an elongated stepextending over the entire angular range of the green body. In the planeof the edge 42 the step has a larger outer diameter than in the oppositeplane. This can be seen in FIGS. 4 c and 4 d. The depth of the recessdesignated with numeral 52 in FIGS. 4 c and 4 d, corresponds to theaverage thickness of the selected grains. If a fine grain size isselected the recess has a small depth 52. If a rough grain size isselected the depth of the recess 52 is larger. In each case the depth 52of the recess is selected in such a way that the thickness of thegrinding wheel is essentially the same over its entire range. Then thegrinding wheels will smoothly lie on top of each other and alwaysrequire the same space for rotation independently of the grain size.

FIG. 4 e illustrates the proportions of the coated green body accordingto the equations:

S _(Be,ges) =S _(Roh)+2'S _(Be) ≦S _(max)

D _(max,S) =D _(Roh,S)+2×S _(Be) ≦D _(housing)

D _(max,S) =D _(Roh)+2×S _(Be) ≦D _(housing)

with the definitions of the variables as shown in the figures andD_(housing) being the diameter of the housing.

If the grinding wheel assembly 18 is installed with the shaft 30 theessentially cylindrical housing portion 16 and—with two grindingwheels—a spacer ring 64 are coaxially mounted on the motor flange 14.

The housing portion 16 is provided with a center bore hole 54. This canbe seen in FIG. 3. The center bore hole is aligned with the bore holes38 of the grinding wheel assembly 18 and the rotational axis of theshaft 30. A disc-shaped recess 58 is provided around the bore hole 54 onthe side 56 facing the motor. A recess 62 is provided on the oppositeside 60 of the housing portion 16. Such recesses 58 and 62 have aboutthe same dimensions as the recess on the side 26 of the motor flange 14.The recesses on the side 26 and the recess 58 form a space in theassembled device. The space serves to accommodate the grinding wheelassembly 18. A spacer ring 64 is provided between the motor flange 14and the housing portion 16 in the embodiment with two grinding wheels asshown in FIGS. 1, 5 and 6. The thickness of the spacer ring 64corresponds to the thickness of one grinding wheel 20 or 22.Accordingly, the difference caused by the additional grinding wheel iscompensated. Independently from the amount of grinding wheels the samemotor flange 14 and the same housing portion 16 with the same recesses26 and 58 may be used in all cases. The grinding angle will not differ.

The recess 62 on the upper side 60 serves as accommodating means for theremoval of grinding left-overs such as dust and grinding chips. Thehousing 16, ring 64 and motor flange 14 also are provided with alongitudinal slit 66 in a radial direction extending over the entirelength of the assembly. The longitudinal slit 66 can be seen in FIG. 1.The slits 66 in the motor flange 14, ring 64 and housing 16 arepositioned on top of each other. The slit 66 formed in such a way iswide enough to let electrodes pass therethrough. The electrode can beshortened at the edge 42 of the or one of the grinding wheels when thegrinding wheel assembly 18 rotates, by cutting the used-up end of theelectrode or the newly shaped electrode end.

The housing 16 and the motor flange 14 are provided with groups 76 and78 of openings in the form of bore holes. The bore holes extend alongthe circumference of the housing 16 and motor flange 14 in the directionof the corresponding end faces in the direction of the grinding wheelnext to the housing or motor flange, respectively. Each group consistsin known manner of a plurality of bore holes with different diameterswhich is indicated above or below the bore hole by an engraving 80. Thiscan be seen in FIG. 6. The angle between an electrode inserted into thebore hole and the grinding wheel is the same for all bore holes in onegroup. For example, the bore hole may have a diameter of 1.6 mm and agrinding angle of 22.5 degrees. The grinding angle for each group isindicated by another engraving above the first engraving. For example,four different angles are possible for a grinding. Electrodes having,for example, 6 different diameters may be used. The electrode is guidedin the bore hole so well that reproducible results can be obtainedwithout difficulty or risk.

More grinding angles, further electrode diameters or the use of agrinding surface with different grain size can be introduced by using amotor flange 14 also having such bore holes 78 and using two grindingwheels as shown in FIGS. 1, 5 and 6. An electrode, for example, can beroughly pre-ground by entering a bore hole in the housing 16. A grindingwheel 20 having a rough grain size is provided with the grinding surfacefacing upwards in the drawing. A bore hole in the motor flange 14 isused for fine grinding. The corresponding grinding wheel 22 with agrinding surface facing downwards is provided with fine grains. The boreholes 76 in the housing portion 16 as well as the bore holes 78 in themotor flange were manufactured with the same machine using identicalsettings. Therefore, the bore holes are identical apart from very smalldeviations. The grinding surface in the present assembly is always inthe same plane. In such a way a particularly small error is made for thegrinding angle. In the present example the bore holes 76 are made insuch a way that the indicated grinding angle is achieved if the grindingsurface is in the plane 60 and the bore holes 78 if the grinding surfaceis in the plane which lays on wheel thickness below the plane 26.

Furthermore, the housing 16 is provided with a group of bore holesextending perpendicular from the upper end to the lower end of thehousing 16. The bore holes of such group also have different diameterscorresponding to the diameters of the remaining groups. The bore holesof the group enable the perpendicular grinding of the electrode tips.

The entire assembly is screwed on a hand-held device. The grinding wheelassembly is positioned directly adjacent to the ball bearing of themotor shaft 30. This avoids rocking at high frequencies.

In order to avoid dust, removed material and grinding material or thelike entering the motor or the bearings a collision disc 84 is provided.The collision disc 84 is mounted between the motor side grinding wheel22 and the motor flange with a sleeve 86 on the upper end 28 of themotor shaft and also rotates. The motor side, lower surface of thecollision disc 84 is positioned in the range of the bottom of the recessin the end face 26. A felt ring 88 is arranged around the sleeve 86which does not rotate. The felt ring 88 avoids further dust, removedmaterial and grinding material to enter the motor or the bearings. Thepin 34 extends through a bore hole in the collision disc 84. In such away not only the grinding wheel assembly 18, but also the collision disc84 is driven by the shaft 30.

The present assembly was explained with reference to two preciseembodiments, one with one and one with two grinding wheels. It isunderstood, however, that the assembly may be varied. It is, forexample, possible to install a further housing portion similar to thehousing portion 16 and to use further grinding wheels in the spaceformed therebetween. Also, different designs of the bore holes forguiding the electrodes are possible.

1. A device for grinding welding electrodes comprising: a grinding wheelwith a grinding range on the surface of the grinding wheel, saidgrinding range coated with a graining material with a selected grainsize; a driving motor and a driving shaft for driving said grindingwheel; and a housing, said housing forming a space, said grinding wheelrotating inside said space and wherein at least one opening is providedin said housing for guiding a welding electrode for grinding in adefined position relative to said grinding wheel, wherein a recess isformed in said grinding range having a selected depth, said depth ofsaid recess being adapted to said grain size of said grinding material.2. The device of claim 1, wherein said surface of said grinding wheelhas an uncoated center range and an edge and wherein said recess extendsfrom said uncoated center range to said edge of said grinding wheel. 3.The device of claim 1, wherein (a) said grinding wheel is provided witha thinner cutting edge, (b) a slit is provided in said housing, saidslit extending perpendicular to said surface of said grinding wheel andwherein said slit is provided for cutting a welding electrode with saidcutting edge, and (c) said cutting edge forms extends in a plane formedby the remaining portion of said grinding wheel in such a way that saidgrinding wheel forms said cutting edge in the range of its circumferencewithout a step.
 4. The device according to claim 1, wherein two grindingwheels are provided, said two grinding wheels laying on top of eachother and having a different grain size.
 5. The device of claim 4,wherein said cutting edge is provided on the side opposite to the otherone of said two grinding wheels.
 6. The device of claim 1, wherein thediameter of said grinding wheel is adapted to said grain size of saidgrinding material.
 7. A grinding wheel for use in a device for grindingwelding electrodes, comprising: a grinding range on the surface of thegrinding wheel, said grinding range coated with a graining material witha selected grain size, the grinding range having a recess formed thereinhaving a selected depth, said depth of said recess being adapted to saidgrain size of said grinding material.
 8. The grinding wheel of claim 7,wherein said surface of said grinding wheel has an uncoated center rangeand an edge and wherein said recess extends from said uncoated centerrange to said edge of said grinding wheel.
 9. The grinding wheel ofclaim 7, wherein (a) said grinding wheel is provided with a thinnercutting edge, (b) said cutting edge forms extends in a plane formed bythe remaining portion of said grinding wheel in such a way that saidgrinding wheel forms said cutting edge in the range of its circumferencewithout a step.